The current version in Ubuntu's repository for 17.10 (2.8.3-3build1) doesn't seem to work for me in Ubuntu 17.10. If I pick "Ubuntu with Xorg" in the login page, then I can start caffeine-indicator, it shows up in the dock at the top right, and its buttons respond correctly, but activating it fails to make any difference in keeping my computer awake.
Version 2.9.4 from the PPA at https://launchpad.net/~caffeine-developers/+archive/ubuntu/ppa works fine (in X). Assuming this issue is widespread and 17.10's version is a dud in the newly default GNOME-based desktop, is it possible for version 2.9.4 (or whatever important patches are in it) to be put into the 17.10 repos?
(If my assumption is incorrect that this problem with the current 17.10-repo version is widespread, and you want to figure out what exactly about 2.9.4 fixes the issue for me so just that could be backported, then I'm willing to help investigate that.)
Note: this bug is an Ubuntu bug, not a Caffeine bug. Caffeine merely happens to be hosted on Launchpad; I don't actually package it for Ubuntu; as you can see, the Ubuntu maintainer is Ubuntu MOTU Developers. Hence, marking invalid for upstream, and adding an assignment to the Ubuntu package.